1. Field of the Invention
The present invention relates to syringes and more particularly concerns disposable syringes having tamper evidence features.
2. Description of Related Information
Generally speaking, a hypodermic syringe consists of a cylindrical barrel, most commonly made of plastic or glass, with the distal end containing a hypodermic needle or adapted to be connected to a hypodermic needle, and a proximal end adapted to receive a stopper and plunger rod assembly. The distal end of the barrel or the needle assembly usually includes the needle shield which removably covers the needle to prevent damage to the needle before use and to prevent accidental needle sticks.
In United States and throughout the world, the multiple use of hypodermic syringe products, which are intended for single use only, is instrumental in drug abuse and more particularly in the transfer of contagious diseases. In addition, drug abusers have been known to remove all or part of the contents of a prefilled hypodermic syringe and replace the missing medicament with water. The needle shield is then carefully replaced so that the subsequent user is not aware that the syringe has been previously used to inject the medication contained therein and/or that the contents have been diluted with water. The subsequent recipient of the injection from such a syringe may suffer the consequences of ineffective drug therapy and may also be infected if the needle was previously used to inject medication.
To remedy drug abuse, drug misuse and contamination problems associated with tampering with syringe assemblies by removing and replacing the needle shield, U.S. Pat. No. 2,371,086 to Watson et al. teaches a hypodermic syringe assembly having a glass needle shield with a zone of reduced diameter and reduced wall thickness that may be sheared to remove the distal end of the needle shield. The device of Watson et al. is also deficient in that it does not allow reshielding because there are no structural elements which will interact to hold the severed portion of the needle shield to the syringe after it is removed. Also in narrow diameter of Watson's needle shield at the point of reduced thickness makes reshielding needle shield, if it were possible, a difficult and possible dangerous process.
U.S. Pat. No. 4,007,740 to Owen also teaches a cannula covering having a frangible section which must be broken to expose the sharpened distal tip of the cannula. The frangible portion which appears only slightly larger in diameter than the needle cannula, once broken, provides evidence of possible tampering or prior use. The narrow diameter of Owen's needle shield in the area of the frangible zone makes it difficult to reshield and increases the probability of the user accidentally sticking himself during the act or reshielding. Also, Owen does not provide structure to hold the severed portion of the needle shield on after reshielding. Accordingly, the needle shield may easily fall off the needle exposing the sharpened needle tip to possibly injure or infect a person handling the used syringe.
U.S. Pat. No. 4,300,678 to Gyure et al. also teaches a needle shield which, at its base is permanently connected to the syringe barrel. The shield also includes a frangible portion adapted to be ruptured so that a first distal portion of the shield is removable from the second portion which remains connected to the barrel. Gyure et al. like Watson et al. and Owen do not provide structure for securely retaining the needle shield on the syringe assembly after use and reshielding. In addition, the normal act of removing the needle shield is to hold the syringe in one hand and the needle shield in the other hand and twist and remove the needle shield. The syringe of the '678 patent, in the alternative embodiment of FIGS. 4 and 5, requires an additional first step of peeling the frangible portion away from the syringe at which point the needle shield may again be gasped in the normal manner for removal of the needle shield.
In U.S. Pat. No. 4,475,903 to Steenhuisen et al. teaches a syringe which is provided with a sleeve of shrinkable plastic material which is shrunk around the needle connection and the barrel. Steenhuisen et al. teach the placement of the shrinkable plastic sleeve so that after the sleeve is broken and the needle guard removed it will be substantially impossible to place the needle guard back to its original position because the broken portion of the sleeve prevents its return.
Although the prior art provides teaching with respect to syringe assemblies having removable needle shields, there is still a need for a syringe having tamper evidence features which does not destroy the needle shield and which allows the option of safe effective reshielding of the needle after injection using the needle shield. There is also a need for syringe assemblies having tamper evidence features which allow removal of the needle shield by holding the syringe barrel in one hand and the needle shield in the other wherein the tamper evidence means can be severed with reasonable rotational or twisting force and in a manner which will not encourage accidental needle sticks, such as by pulling apart the needle shield away from the syringe barrel to sever the tamper evidence means. There is also a need for a separable tamper evidence indicator that may be removed and destroyed at the time of injection while still allowing the option of reshielding but not reassembly of the syringe in its original form because of the missing tamper evidence indicator.